The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Vehicles having hybrid powertrain systems selectively use different energy sources to generate torque and power to achieve optimal fuel efficiency in response to operator commands. This includes selectively employing an internal combustion engine and a motor/generator unit(s) connected to a high-voltage battery module or energy storage system for propulsion and operational control. One hybrid powertrain includes an engine stop/start system wherein the engine automatically stops during ongoing vehicle operation and automatically restarts using an electric motor/generator unit. The system preferably includes a regenerative braking system for recharging the high-voltage energy storage system via the electric motor/generator unit and the ability to selectively shut down the engine during vehicle idle, referred to as an autostop control scheme.
Known motor/generator units may be used in belt-alternator-starter (BAS) systems in place of alternators. The BAS system applies torque to a serpentine belt of the engine when an operator signals an intention to resume travel after executing an autostop control scheme. Torque from the motor/generator unit(s) may be used to crank the engine. During cold starting of the engine, a crankshaft-mounted auxiliary or 12-volt starter motor may provide cranking torque to crank the engine. Known BAS systems use a high-voltage energy storage system supplying high-voltage electrical power through a voltage inverter to the motor/generator unit(s). The high-voltage battery may be temporarily disconnected or otherwise rendered unavailable due to a fault or other operating conditions. This may result in a loss of or an insufficient field excitation, especially for an asynchronous machine-based electric motor/generator unit, which in turn may result in a loss of sustained auxiliary electrical power generation. Insufficient auxiliary electrical power may result in a vehicle shutdown leading to a walk-home event.